Propylene-based elastomers, which may also be referred to as semi-amorphous propylene copolymers or crystallizable propylene-based copolymers, have been employed in the manufacture of fibers and non-woven fabrics. These copolymers are often blended with other polymers in the pursuit of desirable properties.
For example, U.S. Publication No. 2005/0107529 teaches fibers prepared from propylene-based elastomers. Examples 1-4 teach the production of fibers from a melt that contains a 20 MFR propylene-ethylene copolymer containing 15 weight percent ethylene together with a propylene homopolymer. The propylene homopolymer is either a 36 MFR homopolymer or a 400 MFR homopolymer. The fibers are formed by employing a conventional fiber spinning line under partially oriented yarn mode. The fibers and non-wovens prepared therefrom can be heat set to provide durable fabrics.
U.S. Pat. No. 6,218,010 teaches an ethylene-propylene copolymer alloy that is suited for making fibers and non-woven spunbond fabrics having softness at economically acceptable processing conditions. The alloy comprises a random copolymer having an ethylene content of from about 1 to about 5% by weight in an amount of from about 40 to about 90% by weight of the alloy; and a second ethylene-propylene copolymer having an ethylene content of from about 5 to about 40% by weight, in an amount of from about 10 to about 60% by weight of the alloy. The copolymer alloys are described to be prepared by a multi-reactor process comprising a first stage of polymerizing a mixture of ethylene and propylene in single or plural reactors, in the presence of a catalyst system capable of randomly incorporating the ethylene monomers and/or alpha-olefin into the macromolecules to form the random copolymer, and a second stage of, in the further presence of the random copolymer containing active catalyst, polymerizing a mixture of ethylene and propylene in single stage or in plural stages to form the second ethylene-propylene copolymer.
U.S. Pat. No. 6,342,565 teaches soft elastic fiber compositions that include a crystallizable propylene copolymer and a crystalline propylene copolymer such as isotactic polypropylene. The fibers may also include a second crystallizable propylene copolymer. The first crystallizable propylene copolymer is characterized by a melting point of less than a 105° C. and a heat of fusion of less than 45 J/g. The crystalline propylene copolymer may be characterized by a melting point above 110° C. and a heat of fusion greater than 60 J/g. Where a second crystallizable propylene copolymer is employed, it may differ from the first crystallizable propylene copolymer in molecular weight and/or crystallinity content.
U.S. Pat. No. 6,635,715 describes blends of a first isotactic polypropylene homopolymer or copolymer component with a second alpha-olefin and propylene copolymer component, wherein the first isotactic polypropylene component has a melting point above about 110° C., and the second copolymer has a melting point between about 25° C. and 105° C. The blends may have from 2 to 95 wt % of the first component and from 98 to 5 wt % of the second copolymer component. In the examples, the polypropylene used is Escorene® 4292, an isotactic polypropylene homopolymer having a nominal melt flow rate (MFR) of 2.0 g/10 min, and the second copolymer is illustrated by an Mw (weight-average molecular weight) of 248,900 to 318,900 and by a Mooney viscosity (ML (1+4) at 125° C. according to ASTM D1646) of from 12.1 to 38.4. The blends are directed to improved mechanical properties of processing, increased tensile strength, elongation, and overall toughness.